A light-weight portable auxiliary battery pack device for use with portable electronic devices (for example, cellular telephones) includes a rechargeable battery. Such an auxiliary battery pack device may have a slim piggy-back structure and form that fits under and around the sides of a cellular telephone so that the cellular telephone can be slid into the device. The device typically includes a plug connector that engages the main dock receptacle connector of the cellular telephone when the cellular telephone is in place in the device. Examples of such auxiliary battery pack devices are the Juice Pack line of products available from the on-line store of Mophie, LLC at www.mophie.com.
A cellular telephone typically is supplied to the user with an AC-to-DC wall adapter that supplies proper power to the cellular telephone. If AC wall power is available, then the AC-to-DC wall adapter is plugged into the auxiliary battery pack device. The cord and plug of the AC-to-DC wall adapter is used for this purpose. Power from the AC-to-DC wall adapter then charges the battery of the auxiliary battery pack device through the cord. In addition, the cellular telephone may be plugged into the auxiliary battery pack device. If the cellular telephone is plugged into the auxiliary battery pack device, then power from the AC-to-DC wall adapter is also provided through the battery pack device to the cellular telephone through the main dock receptacle connector of the cellular telephone. In this condition, the battery is being charged at the same time that the cellular telephone is operable from AC wall power. If the auxiliary battery pack device is then unplugged from the AC wall adapter or otherwise ceases to receive power, then the auxiliary battery pack device uses its battery as a power source. In some examples, a DC-to-DC converter within the auxiliary battery pack device converts the DC voltage from the battery into a suitably regulated supply voltage for powering the cellular telephone. The cellular telephone is then powered from the battery of the auxiliary battery pack device. From the perspective of the cellular telephone, the cellular telephone is receiving proper DC power through its mail dock receptacle connector just as if the cellular telephone were receiving power from its AC-to-DC wall adapter or from a docking station.
Methods and structures for improving such auxiliary battery pack devices are sought.